1. Field of the Invention
The present invention relates to an organopolysiloxane composition useful as a sealant or the like, the cured product of the composition being excellent in mildew resistance, weather resistance such as resistance to ultraviolet light, and the like.
2. Description of the Prior Art
Since room temperature curable organopolysiloxane compositions capable of curing by moisture contained in the air is easy in handling and the cured product thereof is excellent in weather resistance, they are used in sealants for construction, adhesives in electric and electronic industries, and the like. Particularly, deoxime type room temperature curable organopolysiloxane compositions have a good adhesion to various adherends and also an excellent weather resistance, so that they are used as sealants for places where, for example, in houses, water is often used or a large amount of moisture exists, such as kitchens, bathes and lavatories.
On the other hand, with an improvement in construction techniques of houses in recent years, the air tight properties of houses have been also improved. Thus, said places where in houses, water is often used or a large amount of moisture exists become a suitable habitat for microbes such as mildew. Particularly, mildew inserts its hypha even into the inside of the cured product (silicone rubber) of the composition, so that it is difficult to remove mildew by means of not only wiping but also application of chemicals and the appearance of the cured product is often impaired. In order to prevent the breeding and growth of mildew in the cured products of the compositions, among the room temperature curable organopolysiloxane compositions conventionally used as sealants for places where water is often used or a large amount of moisture exists, there are known compositions in which a mildewproofing agent such as benzimidazole compounds and Zinc Pyrithione has been blended. However, the cured products of the compositions containing a mildewproofing agent have the drawback that they are turned yellow by heating or exposure to ultraviolet light. This inclination is remarkable particularly in the deoxime type compositions using an unsaturated group-containing hydrolyzable organosilane as a curing agent. When the amount of a mildewproofing agent contained in the composition is decreased to an extent in which yellowing does not occur, the mildew resistance of the composition can not be sufficiently exhibited.